Variable output rotating hydraulic machines



Oct. 18, 1966 P. R. LA MAIDA VARIABLE OUTPUT ROTATING HYDRAULIC MACHINES Filed Feb. 17, 1964 5 Sheets-Sheet 1 FIGS INVENTORI PLINE R. LA NIAIDA ww.

w M Attorney 7 Oct. 18, 1966 P.- R. LA MAIDA 3,279,389

VARIABLE OUTPUT ROTATING HYDRAULIC MACHINES Filed Fgb. 17, 1964 5 Sheets-Sheet 2 FIG.3

INVENTOR:

PLINE R. LA MAIDA y a4! W W A TTO RN HY Oct. 18, 1966 R A IDA 3,279,389

VARIABLE OUTPUT ROTATING HYDRAULIC MACHINES Filed Feb. 17, 1964 5 Sheets-Sheet 5 F166 FIG? FIG 4 e9 71 1268 \(YKK a2 87 f3 52 57 7o w as 85 a 0 89 so INVEN'IOR:

PLINF. R. LA MAIDA y L47 I Attorney United States Patent VARIABLE OUTPUT ROTATING HYDRAULIC MACHINES Pline R. La Ma'ida, 5 Rue Leon Cogniet, Paris, France Filed Feb. 17, 1964, Ser. No. 345,278 Claims priority, application France, Feb. 21, 1963, 925,608; July 16, 1963, 941,650

8 Claims. (Cl. 103-161) The present invention relates to hydraulic machines such as pump or motor units and, more specifically, to such machines of the type called radial type, variable delivery plunger machines which include several plungers or pistons moving in radial cylinders arranged in a rotor which is driven in rotation from a main rotating shaft.

In variable delivery hydraulic machines the output may be varied by changing the position of an eccentric, or other mechanism for the same purpose, which so cooperates with the pistons as to change the amplitude of their reciprocating motion according to the choice of said position. A machine of this type is described, for instance, in the US. Patent No. 2,417,183 to J. E. Smith. Although such an improvement considerably increases the usefulness of the machine, it makes it somewhat more difficult to build, owing to the rather critical character of the adjustments and to the additional stress on the working parts which result from the reaction of the eccentric, the operation of which intrinsically involves non-radial forces on the rods or other mechanical parts which drive the pistons.

Moreover, delivery adjustment by eccentricity variation is possible in the case of single piston-stroke per turn machines only.

Other types of variable delivery machines have also been proposed, in which two parallel banks of cylinders and pistons are used, and in which the operation of each such bank may be phase-shifted with respect to that of the other by angularly shifting reaction rings or eccentrics controlling the operation of said pistons. In this case, each cylinder of one bank is interconnected through a passageway with one cylinder of the other bank. The phase-shifting causes the fluid to circulate from one to the other of said interconnected cylinders. The resulting differential action makes it possible to regulate the delivery of the machine by changing the value of the shift angle. However, it is obvious that some power must be dissipated in the between-cylinder circulation of the fluid, and the machines of the kind cannot have a very high efficiency. These machines may be called constant plunger stroke, variable cylinder volume machines since during the time of reciprocation of the plungers, the total volume of two associated cylinders in the banks varies from zero to twice the volume of one cylinder when the two banks are cophasal while this total volume is constant and equal to the volume of one cylinder when the two banks are in phase opposition.

The present invention has for one of its objects an efficient hydraulic machine (pump or motor unit) of the radial cylinder, variable delivery type, in which delivery adjustment may be effected without introducing additional stresses on the main working parts of the machine.

Another object of the invention is a delivery adjustment device which may be applied to hydraulic machines, the adjustment of the delivery of which was not feasible previously, for instance machines operating with several piston strokes for each shaft turn.

To make the understanding of the operation of the machines of the invention easier, it will first be reminded that constant delivery machines of the prior art mainly comprise a rotating shaft, a set of cylinders and pistons driven in rotation from said shaft, and a segment-valve system allowing a unit volume of fluid to be directed toward each cylinder from an inlet passageway and subsequently directed from said cylinder toward an outlet passageway for each piston reciprocation stroke. A driving mechanism directly links the instantaneous position of each piston inside its cylinder with the angular position of the shaft.

The mode of operation of variable stroke machines using the eccentric principle is very similar to that of the constant delivery machines, except for the difference in the driving mechanism for the reciprocating motion of the pistons. In a known system, each piston is coupled to the axle of a roller which is kept in contact with a roller-track borne by a reaction ring fastened to the peripheral part of the machine. This roller track surrounds the main shaft and is so shaped that the distance of its points from the axis of said shaft varies as :a function of their angular position within respect to an origin angular position. The reaction ring is an eccentric in the broads-ense of the word, i.e., it may have the shape of an outcentered circle with respect to said axis, or it may have a different shape, for example an elliptical one.

The machines of the invention also use rollers and eccentric reaction ring, but they essentially differ from the known variable delivery machines in the arrangement of the driving mechanism for the reciprocating motion of the pistons. The machines of the invention are strictly speaking variable stroke machines. Fundamentally, in the machines of the invention, this driving mechanism makes use of at least two rollers (or roller groups) for each piston, and the two rollers (or roller groups) move along corresponding identical but angularly shifted roller tracks provided on at least two different reaction rings spaced apart in the direction of the axis of the main shaft. Adjustment of piston stroke is effected by angular shifting of at least one of said rings with respect to the others.

The two rollers (or roller groups) associated with the same piston are coupled by a swinging-bar, at the central part of which a linking-rod (or other linking member), connecting said central part with the piston, is secured. In fact, said central part is provided with a circular hole and a close-fitting axle inserted therein, and it is the latter axle that is coupled with the linking member and thereby with the piston itself. Obviously, the radial motion of the central part of the swinging-bar drives the piston into an identical and reciprocating motion.

The main advantage of the just-described arrangement is that it provides for a natural balancing out of the parasitic non-radial forces on either of the two rollers (or roller groups) coupled to a common swinging-bar. This much reduces the additional stresses mentioned above in connection with the machines using the eccentric principle. Further, adjustment of the amplitude of the stroke is made much easier, since it can be effected by mere angular shifting of the reaction rings, for instance by leaving one of said rings in a fixed position and displacing the others, or else by displacing one ring in a given rotation direction and the others in the opposite direction. The operation of the device of the invention may e briefly explained as follows:

When the angular shift between the reaction rings is such that the two rollers (or roller groups) coupled to one common swinging-bar constantly rest on parts of their respective roller-tracks equally distant from the axis of the main shaft, each piston and the rollers associated therewith move radially as a single unit; the piston stroke has its full amplitude and the delivery is maximum. When the angular shift between the rings is such that the two rollers (or roller groups) coupled to one common swinging-bar undergo radial displacements in phase opposition, the radial velocity of the center of the swingingbar and of the piston is Zero, each swinging-bar just 05- cillating about a point at a fixed distance from the axis of the main shaft; the delivery then is zero. When the angular shift between the rings is fixed at a value intermediate those corresponding to the just-mentioned extreme cases, the delivery takes a value intermediate zero and the maximum value.

Of course, if more than one roller is associated with one end of a swinging-bar, a corresponding number of roller-tracks and roller rings may be provided. Therefore sets of rings will be occasionally mentioned hereinafter instead of rings.

In a first form of embodiment of the invention, the swinging-bars associated with a roller pair have their longer dimensionor length substantially parallel to planes perpendicular to the axis of the main shaft, and the motion of said bars, as Well as that of the rollers, takes place in such planes.

In a second form of embodiment of the invention, the machine still includes two reaction rings (or ring sets) wit-h corresponding roller-tracks, each cooperating with a plurality of rollers. However, the two rollers (or roller groups) associated'with each other by a common swinging-bar are no longer coupled by a bar substantially parallel to a plane perpendicular to the axis of the main shaft, but by a bar the average direction of the length of which is substantially parallel to that of said axis.

In other words, and for greater simplicity of language, the swinging-bars will be hereinafter described as longitudinal to the motion in the first case, and as transversal to the motion in the second case, since the general motion of the system about the axis of the shaft always remains parallel to said planes perpendicular to the axis of said shaft.

The invention will be better understood from the hereinafter given detailed description, made with reference to the annexed drawings, in which:

FIG. 1 shows in a very schematical form the main features of a theoretical machine, the operation of which simulates that of the devices of the invention;

FIG. 2 schematically shows a first form of embodiment of a machine according to the invention;

FIG. 3 shows in greater detail some parts of the device of FIG. 2; and

FIGS. 4 to 8 are various views of a machine according to a second embodiment of the invention.

Referring first to FIG. 1, given only for explanation purposes, there may be seen in said figure two cr-ankpins rotating in syn-chronism in the same direction 43, driven from a main shaft 57 and mechanically interconnected by an assembly of two differential gears 40 and 50 and a gear-train 53 of 1/1 ratio capable of introducing between said crankpins, by means of a control 54, a phase-shift 2 (p (radians) corresponding to angular shifts (p measured on one and the other side of the common reference direction 44 for each of crankpins 41 and 42, respectively. By means of connecting-rods 45 and 46, crankpins 41 and 42 drive a swinging-bar 47 whose center 48, guided between slide-blocks 49, is rigidly secured to a piston 51 moving in a cylinder 52. Segment-valves 55 and 56 are driven from the shaft 57 whose angular position is the mean position intermediate those of crankpins 41 and 42. These segment-valves open or close when piston 51 reaches the extreme points (inward or outward) of its excursion, as it is well known.

Designating by w (radians per second) the angular velocity of shaft 57, by R the radius of crankpins 41 and 42, and by t the time, the motion parallel to direction 44 of the end 58 of swinging-bar 47 may be represented by R. cos (a: t while that of the other end '59 of the same swinging-bar may be represented by R cos (w i-I-qo). This is valid as an approximation, assuming levers 45 and 46 to be long enough in comparison with R. The motion of the center 48 of 47 in the same direction 44 may be represented by R cos 30. cos a: t.

Consequently, a variation in the angle ga results in a variation of the stroke of the piston 51 and consequently of the apparent (i.e., useful) volume of cylinder 52, the piston stroke and the useful volume of the cylinder being possibly reduced to zero by giving q: the value 1r/2 radians (ie, degrees).

By giving to a value between 90 and degrees, and assuming the segment-valves to be driven in the same time relation as before, the direction of flowing of the fluid will be reversed (in the case of a pump), or the rotation direction will be reserved (in the case of a motor).

FIGS. 2 and -3 show the actual arrangement of a machine embodying the just-mentioned principles. This machine is essentially a rotary hydraulic machine with seven cylinders and four piston strokes per turn, in which each piston is driven from two rollers or pairs of rollers which themselves drive a swinging-bar, each such roller or roller pair having its own roller-track (or tracks).

In FIG. 2, there may be seen a star-assembly 13 of cylinders 8, 9, driven in rotation from the main shaft of the system; in every one of these cylinders is provided a piston such as 10. A cylindrical, non-rotating pintle 5 and a cylindrical jacket 7 rotating as a single unit with the cylinder assembly 13, ensure that the fluid be distributed through openings such as 14, 15, and passageways 16 and 17 bore in the cylindrical pintle 5. Such a distribution system is well known in the art and is fully described with relation to FIGS. 4 and 6. However, in the machines of the known art, each piston was directly set in motion by a roller individually associated therewith, or by a pair of rollers directly acting thereupon. In the here described machine, on the contrary, there is associated with each piston a swinging-bar such as 20 which is capable of oscillating about a short axle 21 rigidly con-' nected with the corresponding piston. Each swingingbar such as 2i) forms the longitudinal member of a carriage (FIG. 3) comprising four rollers associated in pairs on axles of unequal lengths. Rollers 24 and 25, mounted on the shorter axle 23, roll on the roller-track of reaction ring 26 on one and the other side of which are located the roller-tracks of reaction rings 27 and 28 on which roll the rollers mounted on the longer axle 22. Arrangements similar to those found in the machines of the known art ensure that the rollers be kept in contact with their roller-tracks. These arrangements have not been shown in FIGS. 2 and 3, to avoid the inconvenience of a too much complicated drawing but they are shown in FIGS. 4 and 6. The three rings 26, 27 and 28 have a common shape as to their roller-tracks, with a rotation symmetry of an order equal to the number of piston strokes per turn of the main shaft, that is four in the present case. The rings may be rotated about the main axis of the machine (FIG. 3). Such rotation is effected by operating a crank-handle 34 directly driving ring 26 through a pinion 31 itself driving a toothed-rack 32 and simultaneously driving the two rings 27 and 28 through a gear-train 33. In that way the outer rings rotate simultaneously with the inner one, but in the reverse direction.

It will easily be understood that, by giving the two outer roller-tracks on one hand, the inner roller-track on the other hand, an angular shift corresponding to the are covered by the swinging bar 20, or rather more exactly to that covered by the distance between axles 22 and 23, the rollers mounted on said axles bear at any instant on portions of roller-tracks having similar profiles. During the rotation of the star-assembly, the swinging-bars do not oscillate about their center 21, and the machine operates like a conventional constant delivery machine. This corresponds to the case where (p is zero in the formerly mentioned formulae. Now, if an angular shift equal to one half of the angular repetition period of the rings is introduced, the radial motions of the axles will be in phase opposition with each other. This corresponds to the case of to equal to 90 degrees in the formulae. The. delivery of the machine then becomes zero. For the intermediate adjustments of the crank handle 34, the delivery may take any value between zero and the maximum value. When (p is larger than 90 degrees, the delivery, i.e., the pump acts as a hydraulic motor and becomes negative.

It must be precise-d that the angle (p which intervenes in the formulae generally differs from the half of the physical angle by which the two ring sets (and the corresponding roller-tracks) are shifted with respect .to each other. In fact the angle to is equal to the product of the latter half-angle .by an integer number equal to that of the piston strokes per shaft turn, i.e., four in the case of FIGS. 2 and 3.

A second and somewhat preferable form of embodiment of the invention will now be described. It improves over the already-described one in that it is more easily built and, at the same time, in that its mode of operation is closer to the theoretical one.

Generally speaking, as already mentioned, this embodiment differs from the previously described one in that the motion of the swinging-bars takes place in planes substantially passing through the axis of the main shaft, instead of in planes perpendicular thereto. Such motion may thus be described as transversal to the general plane of the reaction rings, instead of being parallel thereto.

More precisely, in the latter embodiment of the invention, the driving mechanism consists of two reaction rings each provided with a roller-track and with each of which a plurality of rollers is associated. The rollers of one and the other of said pluralities are coupled in pairs by transverse swinging-bars, the center of each of which is connected with one of the pistons of the machine so as to permit a slight rocking action, while its ends slide in a cylindrical recess provided in a swivel-joint inserted in each roller.

The arrangement will be better understood by referring now to FIGS. 4 to 8. The machine that will now be described is essentially a rotating machine with seven cylinders and four piston strokes per turn, in which each piston is driven from two rollers through a swinging-bar, each roller having its own roller-track.

Referring first to FIG. 4, there may be seen a cylinder star-assembly rotor 60, one cylinder being shown at 61. in each one of said cylinders is provided a piston such as 62. The rotor is driven by a drive shaft member 88 which is connected thereto by means of a coupling member 89 and a cylindrical extension or jacket 64. This jacket embraces -a stationary or fixed pintle 63 formed with a central bore for the passage of the driving shaft and with peripheral longitudinally extending passageways 16 and 17. As the pistons reciprocate four times per rotor turn, there are four inlet passageways 16 and four outlet passageways 17 imbricated with one another. Inlet and outlet ports are formed through the walls of the pintle communicating with their respective passageway and located at the two ends of the passageways. Inlet ports 96 and 96' communicate with inlet passageways 16 and outlet ports 97 and 97' communicate with outlet or pressure passageways 17. The ports 96' communicate with an annular chamber 98 and an inlet bore 94 leads from a supply tank (not shown) to this chamber. The ports 97 communicate with another annular chamber 99 and an outlet bore 95 leads to a work mechanism (not shown). All of the ports 96 and 97 (eight on the whole) liein the same transverse position and cyclically communicate with the cylinders through ports 65 formed in the bottom wall of the cylinders as the cylinder star-assembly rotates around the stationary pintle directly controlled by a roller or a pair of rollers associated therewith, in the here described machine, on the contrary, there is associated with each piston a swinging-bar such as 70 which may oscillate about a short axle 67 rigidly coupled with the corresponding piston. The ends 68 and 69 of the swingingbar 70 may slide inside the swivel-joints 72 and 73 housed in the central parts of rollers 74 and 75. Each roller,

74, for instance, is mounted on a support 71 (FIGS. 4 and 6) which may slide between guide-blocks such as 76. Thus, in addition to its rotation motion about an axis parallel to that of the main shaft of the machine, roller 74 moves in a radial motion which, combined with that of roller 75, imparts a more or less pronounced motion to piston 62.

A roller, such as 75 for instance, is shown on a larger scale in FIG. 8. It comprises a swivel-joint 73 in which the end of swinging-bar slides, a shell 77 made of two hemispherical parts fitting 73, an inner ring 78, a frame 71 sliding between the guide-blocks 76 (not shown in FIG. 8), two outer rings 79 and 80, respectively, located on one and the other side of frame 71, and, between the inner and outer rings, a needle-bearing 81. The inner ring 78 is fastened to frame 71.

Rollers 74 and (FIG. 4) roll on the roller-tracks of rings 82 and 83, which are of identical shape, with a rotation repetition symmetry of an order equal to the num ber of piston strokes per shaft turn, that is four in the present instance. Rings 82 and 83 may be angularly shifted about the axis of the machine. The arrangement for this purpose is shown in FIGS. 4 and 5. Angular shifting is obtained by means of a crank-handle 85 (FIG. 5) directly driving ring 83 through a pinion 85 and indirectly driving ring 82 through an inverting gear 87. Thus the rings may be angularly shifted in opposite directions.

FIGS. 6 and 7 show two other views of the machine. FIG. 6 illustrates the manner in which the rollers are kept in place between the guide-blocks such as 76, and how they are pressed on the rings by means of springs. FIG. 7 is a view of the roller and swinging-bar system as seen from the outside of the machine in a radial direction.

It will easily be understood that, if the rings are given a zero angular shift, rollers 74 and 75 (FIG. 4) move at any instant in an identical manner in the radial direction. During the rotation of the cylinder-assembly, the swinging-bars do not oscillate about their center, and the machine operates like an ordinary constant-delivery machine. This corresponds to a zero value of (p in the above-given equations. If opposite angular shifts equal to one-fourth of the angular repetition symmetry period is now given to the rings, the rollers will move radially in opposite phases. This corresponds to the -degree value of (p in the equations, and the delivery of the machine becomes zero. For intermediate adjustments of crank-handle 84 (FIG. 5), the delivery will take any value between zero and the maximum. When exceeds 90 degrees, the delivery becomes negative and takes its maximum absolute value when (p is equal to degrees.

The shape of the rings is largely optional; its choice mainly depends on practical considerations. A sinusoidal variations of the inner radius of the ring as a function of the angle may, for instance, be adopted.

What is claimed is:

1. A variable stroke radial cylinder hydraulic machine, comprising a main rotating shaft having a fixed axis, a plurality of cylinders driven in rotation from said shaft and each provided with a piston, fluid ports formed in said cylinders, a stationary pintle coaxial with said shaft, fluid passageways and ports formed in said pintle, said pintle ports registering with said cylinder ports in time succession, first and second sets of reaction rings positioned around and spaced apart along the direction of said fixed axis and each provided with a roller-track the distance of the points of which from said axis varies as a function of their angular position around said axis, control means for angularly shifting around said axis at least part of one of said sets of rings with respect to the other, and a driving mechanism for at least part of said pistons comprising a first and a second plurality of rollers, means for causing said first and second roller pluralities to respectively bear upon corresponding roller-tracks on said first and second sets of reaction rings, a plurality of swinging bars each having one of its ends mechanically linked with at least one roller of said first roller plurality and the other of its ends mechanically linked with at least one roller of said second roller plurality, and a mechanical connection coupling the central part of each of said swinging-bars to one corresponding of said pistons.

2. In a hydraulic machine .as claimed in claim 1, the arrangement in which said mechanical connection includes an axle provided in said central part of each of said swinging-bars, said axle being linked with said corresponding one of said pistons.

3. A variable stroke radial cylinder hydraulic machine, comprising a main rotating shaft having a fixed axis, a plurality of cylinders driven in rotation from said shaft and each provided with a piston, fluid ports formed in said cylinders, a stationary pintle coaxial with said shaft, fluid passageways and ports formed in said pintle, said pintle ports registering with said cylinder ports in time succession, first and second sets of reaction rings positioned around and spaced apart along the direction of said fixed axis and each provided with a roller-track the distance of the points of which from said axis varies as a function of their angular position around said axis, control means for angularly shifting around said axis at least part of one of said sets of rings with respect to the other, and a driving mechanism for at least part of said pistons comprising a first and a second plurality of rollers, means for causing said first and second roller pluralities to respectively bear upon corresponding roller-tracks on said first and second sets of reaction rings, a plurality of swingingbars each having one of its ends mechanically linked with at least one roller of said first roller plurality and the other of its ends mechanically linked with at least one roller of said second roller plurality, and a mechanical connection coupling the central part of each of said swinging-bars to one corresponding of said pistons; wherein each of said swinging-bars moves in a plane substantially perpendicular to said fixed axis.

4. A variable stroke radial cylinder hydraulic machine, comprising a main rotating shaft having a fixed axis, a plurality of cylinders driven in rotation from said shaft and each provided with a piston, fluid ports formed in said cylinders, a stationary pintle coaxial with said shaft, fluid passageways and ports formed in said pintle, said pintle ports registering with said cylinder ports in time succession, first and second sets of reaction rings positioned around and spaced apart along the direction of said fixed axis and each provided with a roller-track the distance of the points of which from said axis varies as a function of their angular position around said axis, control means for angularly shifting around said axis at least part of one of said sets of rings with respect to the other, and a driving mechanism for at least part of said pistons comprising a first and a second plurality of rollers, means for causing said first and second roller pluralities to re-.

spectively bear upon corresponding roller-tracks on said first and second sets of reaction rings, a plurality of swinging-bars each having one of its ends mechanically linked with at least one roller of said first roller plurality and the other of its ends mechanically linked with at least one roller of said second roller plurality, and a mechanical connection coupling the central part of each of said swinging-bars to one corresponding of said pistons; wherein each of said swinging-bars moves in a plane substantially passing through said fixed axis.

5. In a hydraulic machine as claimed in claim 1, the arrangement in which said control means include gear means for'respectively shifting said first and second sets of rings by equal angles in opposite directions.

6. In a hydraulic machine as claimed in claim 3, the arrangement in which each of said swinging-bars has one of its ends mechanically connected by a short axle to a first pair of rollers and the other of its ends mechanically connected by a longer axle to a second pair of rollers, and in which said first and second pairs of rollers respectively roll on tracks provided on said first and second sets of rings.

7. In a hydraulic machine as claimed in claim 6, the arrangement in which said first pair of rollers rolls on a common track and in which one and the other of said second pair of rollers respectively roll on two tracks located on one and the other side of said common track along the direction of said axis.

8. In a hydraulic machine as claimed in claim 4, the arrangement in which each of said swinging-bars has each of its ends mechanically connected with a roller by means of a swivel-joint.

References Cited by the Examiner UNITED STATES PATENTS 2/1950 Hofier 103161 2/1959 Mergen et al. 103-37 

1. A VARIABLE STROKE RADIAL CYLINDER HYDRAULIC MACHINE, COMPRISING A MAIN ROTATING SHAFT HAVING A FIXED AXIS, A PLURALITY OF CYLINDERS DRIVEN A ROTATION FROM SAID SHAFT AND EACH PROVIDED WITH A PISTON, FLUID PORTS FORMED IN SAID CYLINDERS, A STATIONARY PINTLE COAXIAL WITH SAID SHAFT, FLUID PASSAGEWAYS AND PORTS FORMED IN SAID PINTLE, SAID PINTLE PORTS REGISTERING WITH SAID CYLINDER PORTS IN TIME SUCCESSION, FIRST AND SECOND SETS OF REACTION RINGS POSITIONED AROUND AND SPACED APART ALONG THE DIRECTION OF SAID FIXED AXIS AND EACH PROVIDED WITH A ROLLER-TRACK THE DISTANCE OF THE POINTS OF WHICH FROM SAID AXIS VARIES AS A FUNCTION OF THEIR ANGULAR POSITION AROUND SAID AXIS, CONTROL MEANS FOR ANGULARLY SHIFTING AROUND SAID AXIS AT LEAST PART OF ONE OF SAID SETS OF RINGS WITH RESPECT TO THE OTHER, AND A DRIVING MECHANISM FOR AT LEAST PART OF SAID PISTONS COMPRISING A FIRST AND A SECOND PLURALITY OF ROLLERS, MEANS FOR CAUSING SAID FIRST AND SECOND ROLLER PLURALITIES TO RESPECTIVELY BEAR UPON CORRESPONDING ROLLER-TRACKS ON SAID FIRST AND SECOND SETS OF REACTION RINGS, A PLURALITY OF SWINGING BARS EACH HAVING ONE OF ITS ENDS MECHANICALLY LINKED WITH AT LEAST ONE ROLLER OF SAID FIRST ROLLER PLURALITY AND THE OTHER OF ITS ENDS MECHANICALLY LINKED WITH AT LEAST ONE ROLLER OF SAID SECOND ROLLER PLURALITY, AND A MECHANICAL CONNECTION COUPLING THE CENTRAL PART OF EACH OF SAID SWINGING-BARS TO ONE CORRESPONDING OF SAID PISTONS. 